The actual sound environment system exhibits various types of linear and non-linear characteristics, and it often contains an unknown structure. Furthermore, the processes observed in the sound environment inevitably contain observation noise or uncertain factors. In this paper, a method for estimating the specific signal for a sound environment system with unknown structure and observation noise of unknown statistical property is proposed by introducing a system model of the conditional probability type. The effectiveness of the proposed theoretical method is confirmed by applying it to the actual problem of signal estimation of the sound environment.